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Retrofit in Hull

September 13th, 2015. SuperHomes"Opening doors to low energy refurbishment" The homes, which achieve at least 60% less CO2Carbon dioxide is a gas which is given off when carbon based materials such as fossil fuels (coal, oil, and natural gas) are burned. It is called a greenhouse gas because it works like the glazing of a greenhouse and causes global warming emissions, have open days. see the Supehomes website open day at 84 Inglemire Avenue, Hull.

Thanks to the lovely couple who live there and opened their home to inspire others on the Superhomes open day in 2015. This is one of the very few such initiatives in the area.

Their house is a 1930s semi with solid brick walls and and a (probably) 1970s rear extension with cavity walls (which they insulated with poured polystyrene bead)

Retrofitting an average 1930s semi must be one of the most difficult projects to undertake, particularly in terms of where the priorities lie. This project incorporates a wide range of retrofit features including

considerable amounts of insulation including external and internal

attention to air tightnessA measure of how leaky a building is to air. In other words, how draughty it might be. There are now standard fan pressure tests to check how air tight a house is and the Building Regulations have minimum standards for all new houses (L1A – Conservation of fuel and power in new dwellings (England)). A much higher degree of air tightness is covered by the Passivhaus standard

large increase in loft insulation (up from 100mm to 300mm of mineral wool)

an air source heat pump (more on that below)

a sensible approach to conserving worthwhile aspects of the building which were attractive or didn’t need replacing (most of the floor boards, skirtings, architraves, existing double glazed windows etc.

a limited amount of ventilation heat recovery

both pvPhoto Voltaic. referring to the generation of electricity from sunlight and evacuated tubeReferring to thermal solar collectors. There are two types of thermal solar collectors (usually used to heat water), - "evacuated tube" and "flat plate" solar colectors

care about sourcing materials and building skills, locally where possible

using natural paint and varnish finishes

low water shower head to save water and water butt to water the garden

a wood burning stove for the sheer joy of it.

The wall insulation is possibly the most interesting part of this project because of its complexity and their considered approach to it:

The front and back walls have been insulated internally while the end wall has the insulation applied externally. Compared with building a new house there are many complexities and compromises involved with insulation.

see more on retrofit insulation

External insulation is best (and lots of it) but there are some other factors at work:

If they had externally insulated the front wall it would have jutted out (maybe 200mm or 300mm) compared with the neighbour’s house, due to the extra insulation thickness. How would planning (permission) view this and how would it look? Another factor involved with this project was that the owners like the look of traditional brick rather than render which normally goes on external insulation. Well of course that’s a matter of personal taste. Render could become the new signifier of eco insulation just as stuck-on concrete stone tiles once became the signifier of someone who wanted to distinguish their newly purchased council house from those around. The back wall probably doesn’t matter visually quite so much so it’s easier to insulate that externally anyway.

When you insulate externally you have to allow for the effect of extra wall thicknesses. For instance, at the most obvious, your roof may no longer extend over the walls and will need extending too. This can create problems in itself especially if the bedroom windows are very close to the eaves. Window sills will need altering and there might be some really tricky areas such as in the picture below where the extra insulation and render meant that a narrower door had to be used in the side extension.

Internal insulation – there are three main considerations:

the more insulation you add, the smaller the rooms get. This can be quite significant,

you need to do extra side insulation on the internal walls (about a metre in length) so that they do not become heat loss routes (because they connect directly with the external walls). This can create an awkward step in the internal wall[for the purposes of part E of the Approved Documents] - Any wall that does not have a separating function..

it will damage internal room decorations or features. So the decider here is whether the rooms need keeping as they are or whether they would be better for replastering etc.

Energy-wise, an interesting balance has been struck. Huge savings have been made on the energy bills, not only on heating but also via solar panels, LED lighting and appliances. Check out their web site which gives figures on savings, particularly on CO2 emissions.

The problem with retrofit is about where exactly do you spend your money and how far do you go with it? Arguably, in the case of this house, it might have been better to “go the whole hog” and achieve the EnerPHitthe Passivhaus standard as applied to refurbishment of an existing house. It makes allowance for the difficulty of bringing older properties up to a high thermal standard. see Passivhaus refurbishment standard if sufficient funds had been available. A complicating factor is the Renewable Heat Initiative, which favours add-ons such as solar collectors and heat pumps rather than the “Fabric First” approach which is mainly about insulation.

The space heatingthe heating of the rooms as opposed to the heating of the domestic hot water. See Space heating and Domestic hot water is now provided by an air source heat pump which doesn’t come cheap. At about £11,500 (including its hot water storage tank), this has been used to replace the ageing gas boiler. It should have a COPCoefficient Of Performance. Applied to heat pumps (in heating mode) this indicates the ratio of how much energy they can shift compared with how much they use to do it. So for instance, a ground source heat pump with a COP of 3 will be able to get 2kWh of heat out of the ground for every 1kWh it uses. So it gives out 3kWh when you include the heat off the pump itself. The COP in cooling mode is calculated differently since the heat off the pump is not useful. of about 3 but will probably not make any carbon savings over a gas boiler (since it runs on electricity – which is inefficient to produce). These bits of kit are not cheap to maintain either; annual service costs are around £300 compared with £200 for a gas boiler.

air source heat pump

It is interesting to speculate what the outcome might have been if the money spent on the ASHP had gone into extra heat insulation, extra draft proofing and PassivhausSee more on the Passivhaus standard. The PassivHaus Institute has pioneered a standard for low energy buildings. It includes very low energy usage and ways of achieving this. The word is derived from the idea of buildings which are fundamentally low energy and passive solar heated rather than using extra gadgets to heat them. See Passivhaus for the UK branch of the organisation. standard MVHRMechanical Ventilation with Heat Recovery. This is usually a double fan arrangement which extracts stale air from the house and sucks in fresh air at the same time. As the warm stale air is blown out, heat is extracted from it and passed over to the cool incoming air by means of a heat exchanger. With the latest technology, over 90% of the heat can be recovered. (see Passivhaus standard)
(at about £3750). Possibly it could have achieved EnerPHit standard for the same expenditure.

The interesting thing about Enerphit is that when you get to that high a standard of insulation, a central heating system becomes unnecessary. The little heat needed is injected straight into the ventilation system. Along with solar gain, body heat and heat from appliances, this is enough to provide a high level of heating. See the Europhit web site.

Back to the insulation! A decision was made to retain the appearance of the front and rear of the house by insulating on the internal surfaces of the walls (40mm of wood fibre board), whereas the end wall was insulated externally and rendered. There were no planning permissionthe legal basis for being allowed to do some form of development such as building a house. (not to be confused with Building RegulationsThese are the mass of regulations that cover safety, health, welfare, convenience, energy efficiency etc. in the way buildings are constructed. Not to be confused with Planning consent (which is more to do with whether you can put up the building in the first place). See more on the regulations which are all about whether the building is properly constructed). see more on Planningthe legal basis for being allowed to do some form of development such as building a house. (not to be confused with Building Regulations which is all about whether the building is properly constructed). see more on Planning objections to this. But what happens when you insulate internally is that any internal walls which are directly connected to external ones provide a ready path for heat to escape.

The way to prevent this is to add insulation to the internal wall for about a metre back from the connection to the outer one. This is what they did.

This of course creates an uneven internal wall finish. A more radical approach is to cut the internal wall away from the external one and fill the gap with insulation. If you do this you will need advice from a structural engineer as the junction between internal and external walls is often used for structural integrity.

The end wall insulation (100mm fibreboard with render), also posed some challenges. It has a capping piece where it extends out beyond the roof overhang and gutter

and its thickness also caused the door on the lean-to extension to need narrowing at the back of the house.

A narrower door due to the thickness of the wall insulation. Note also the rainwater harvesting connection to the fall pipe.

Solar energy

With help from the Renewable Heat Incentive, both PV and solar thermal panels have been installed. An interesting aspect of the pv panels is that they are on three sides of the roof and that a redundant chimney was taken down to prevent overshadowing of the panels. Micro inverters are incorporated in the pv circuitry.